minimum frequency with 4472

[Kallis]

Hello,

While going thru the specs of 4472, I found that there is some 3.4Hz -3db cutoff frequency in the amplifier characteristics. Does this mean that if my signal is having a frequency of .5Hz, I will not be able to measure it? If not, anyone has any clue what this means?

TIA

Kal

[Ian_Ren]

I think if you set couple to DC, then the filter is by-passed.

[preston_johnson]

Yes, with DC coupling, the AC coupling high pass filter is bypassed. So if you are not providing IEPE power you can DC couple your signal.

The 4472B model of the board has a 0.5Hz AC coupling filter. So this may be a choice if you are measuring vibration, rather than acoustical measurements.

[crimolvic]

preston, do you know where I can find information about what kind of High-Pass filter does the 4472 and 4472B use?, I mean if it is buttherworth, Bessel, etc, and maybe the curve graphs

[preston_johnson]

Yes, the best filter documentation is in the manual for the 4472 and 4472B. 

see:

http://digital.ni.com/manuals.nsf/websearch/E7968CA4F4FF9D1686256A57004FFC5E

See the filter section of the manual, page 3-4.

Let us know what additional questions you have.

[crimolvic]

Yes Sr. but there is information about the Low Pass filter, I need information about the High Pass filter used for the input coupling when is seted to AC. I know that this is performed by the connection of a HighPass filter that has a cutoff of 3,4 Hz(-3dB) for the 4472 and 0,5 Hz for the 4472B. I need to know wich kind of filter is this (Butterworth Xpoles; Bessel, usw.)

Thanking you in advance, Mr. Preston Johnson

[preston_johnson]

sorry about that,

the high pass filter is described in the manual, briefly.  It does not say what kind of filter, but discribe its -3db point.  See page 2-9

http://digital.ni.com/manuals.nsf/websearch/06620B18F6A9F0F686256CFD00821ACA?OpenDocument&node=13210...

I'll ask our product support engineering to comment. 

Preston

[Jack_A.]

Here's a little more info on the filter:

Each input channel on the NI 447X is equipped with a two-pole lowpass Butterworth filter. The analog filter cutoff frequency is about 400 kHz. This filter has a gradual rolloff with very little attenuation for any frequencies within the 45 kHz input bandwidth of the NI 447X. The high cutoff frequency of the filter guarantees extremely flat amplitude response and minimal phase error for signals of interest.

Hope this helps,

-Jack

[Jack_A.]

Sorry...Ignore what I just posted (I think it was a little too early in the morning for me).  I put the info that you already know about the lowpass filter in there....I'll post back with some info on the high pass filter.

-Jack

[crimolvic]

No problem Jack, it happens to all of us.

greetings

cjmv